The current trend in microelectronic packaging is toward high performance applications which demand both a higher density of electronic functionality and functionalities which operate at higher speeds. Producing electronic packages which operate reliably and meet these demands of high performance applications is a challenge facing the microelectronic industry. One particularly difficult aspect of producing such packages is producing joints or bonds in multilayer packages between metallized components such as pins, leads, or heat sinks and ceramic substrates. These joints or bonds must have the mechanical durability, electrical conductivity and heat dissipation necessary to ensure reliable performance under the varying and extreme conditions encountered in high performance applications. Further, the process or method of joining the metallized components to the ceramic substrate must be as cost effective and simple as possible.
Currently in multilayer electronic packaging, there are several methods for attaching metallized components to ceramic substrates. The attachment method used is dependent upon the type of multilayer package being fabricated. For high temperature cofired systems which use alumina-based dielectric layers and tungsten or molybdenum metallizations, a brazing method is used for attachment. The brazing is carried out at a temperature of about 840.degree. C. in a hydrogen-nitrogen atmosphere. This method results in good bond strengths and allows for temperature latitude in subsequent processing.
Low temperature thick film or cofired dielectric sheet systems use glass and alumina-based dielectrics and gold, silver or copper metallization. Brazing has not been successful with low-temperature systems because the temperatures of firing and brazing are essentially the same. This creates a condition where, during the brazing operation, the braze attacks the previously formed bond between the metallization and the ceramic, causing the metallization to separate from the substrate. A disruption of the electrical conductivity results rendering the package useless. Common methods of attachment which are used in lieu of brazing for these low temperature systems include soldering, wirebonding and welding, such as thermal compression and parallel gap welding.
Both of the foregoing systems including the respective methods of attachment are currently in use. However, these systems suffer from some disadvantages in high performance applications. In the high-temperature cofired packages, the electrical conductivity of the metallizations formed with tungsten and molybdenum is not as high as desired for high performance applications. In the low-temperature packages, the conductivity of the gold, silver or copper metallization is good, but the bond strengths are typically lower than those obtained by brazing and are not as high as desired for high performance applications. In addition, solder joint integrity can be lost during some subsequent processing operations.
There existed a need, therefore, for a process for brazing metallized components to low-temperature multilayer packages in order to obtain a package which had both high conductivity and good bond strength of metallized components. Such a brazing process has been developed and disclosed in U.S. Pat. No. 5,033,666. However, it was found that many standard gold conductor compositions did not adhere as well as other metal conductor compositions when used in such a brazing process. It is therefore an object of this invention to provide gold conductor compositions which can be used in a process for brazing metallized components to low temperature multilayer ceramic packages resulting in improved bond strengths and package integrity.